A transformer is an electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. A varying current in one winding (e.g., inductor or coil) of the transformer produces a varying magnetic field, which in turn induces a voltage in a second winding. Power is transferred between the two windings through the magnetic field, without a metallic connection between the two circuits. Transformers may be used to increase or decrease the alternating voltages in electric power applications.
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted.